1. Field of the Invention
The present invention relates to a device which can be used to fit in a reversible way a mechanical component equipped with a cylindrical hub onto a cylindrical shaft, and in particular to a device that allows a tractor roller for yarn, usually of a plastic material, to be fitted onto a metal shaft which is circular in section.
2. Background Art
Devices have been known some time that allow the reversible fitting of mechanical components with conical bores onto cylindrical shafts by means of a split or bushing with cylindrical internal surface and conical external surface. A groove on the external surface of the bush allows the same bush to be fixed to the hub by screws or grub-screws, while a keyway is cut into the internal surface of the bush and the external surface of the shaft to allow the bush to be keyed to the shaft.
However, the laboriousness of the operation to produce the keyways and the play that results, with time, between hub and shaft, make this solution unadvisable, particularly if the mechanical component is of plastic material.
Friction-fitting devices have also been known for fitting mechanical components with cylindrical bores, comprising at least one pair of conical split bushes, which bear respectively on the hub and on the shaft involved in the fitting.
To allow the transmission of a torque via friction, these devices must develop considerable radial forces that bear against the hub of the mechanical component. Therefore, such fitting devices require mechanical components with hubs that are very large in relation to the shaft diameters. They could also present dismantling problems due to the two bushes jamming onto the surfaces with which they are in contact.
An alternative technique widely used particularly for fitting yarn tractor rollers onto metal shafts consists of the provision of a plurality of threaded through-holes disposed radially along the external surface of the roller to accommodate pressure screws, which exercise a force on one piece by means of their end while the screw stem is screwed into a threaded hole in the other piece. When tightened the screws hold the shaft securely creating a detachable coupling of the roller to the same shaft.
However, this solution, which is adequate for the transmission of low torques between shaft and hub, has the drawback that it is difficult to center the mechanical component precisely on the shaft and therefore does not allow a correct balancing of the roller in motion. A further, but no less significant, drawback is that the screw holes accommodating the screws could damage the same yarn by acting as an impediment to the free sliding of thread.